Tube fired radiant energy heater systems are frequently used in industrial and commercial buildings which are difficult to heat. In such applications, radiant energy heating systems are regarded as superior to forced air systems from the stand points of the economy and comfort in minimizing the stratification of heat from top to bottom in a building and in fuel savings. Tube fired radiant heaters radiate heat downwards towards the floor thereby heating the floor and taking advantage of the natural convection of heat from the bottom to the top of the interior of the building.
Tube fired radiant heating systems normally include a burner mounted at the inlet end of an emitter tube which radiates heat along its length to the exhaust and of the emitter tube wherein the combustion products are naturally vented away into the atmosphere. The temperature of the emitter tube naturally varies from the inlet end to the exhaust end, the hottest end being nearest the combustion flame of the burner at the inlet end and the coolest area of the emitter tube normally being the exhaust end where the exhaust gases are vented to the atmosphere. This results in an undesirable temperature profile (or temperature drop) along the emitter tube, the inlet being the hottest end of the emitter tube and the exhaust end being the coldest part of the emitter tube. Most indoor heating systems strive to produce as uniform as possible, temperature distribution throughout the building that is being heated. Unfortunately the temperature profile that is present in most radiant tube emitters creates non uniform heating along the length of the emitter tube and therefore, non uniform temperatures throughout the building that is being heated.
The problem is further exacerbated the longer the emitter tube being supplied with heat from a single burner. Therefore, building configurations which are long and narrow requiring long emitter tubes are particularly susceptible to a larger temperature profile from the inlet end to the exhaust end in a radiant tube heater system.
Some attempts have been made to minimize this problem and in particular U.S. Pat. No. 4,529,123 filed by Arthur C. W. Johnson on Sep. 2, 1983 and issued on Jul. 16, 1985 and assigned to the Combustion Research Corporation describes an attempt to minimize the temperature profile along a radiant heater emitter tube. U.S. Pat. No. 4,529,123 utilizes an insulated sleeve along the inlet portion of the emitter tube in order to reduce the amount of heat transferred to the emitter tube along the first portion of the emitter tube. The Patent discusses insulating materials such as magnesium oxide, aluminum oxide, ceramic materials, solid materials, glomerate fired and/or laminated sheets. Preferably the use of a ceramic insulator material is recommended which is manufactured by Carborundum Corporation under the Trademark Fiberfrax.TM.. The patent disclosures that a more uniform temperature distribution along the emitter tube is achieved by using insulated sleeves however, a number of drawbacks have been experienced using this type of insulation method. In commercial practice the insulating material within the emitter tube tends to erode preferentially in certain areas due to direct impingement of the burner flame onto the insulating material and/or local hot spots caused by either small imperfections within the insulating material and/or in and around areas where connections in the insulating material have been made. Where a local hot spot develops in the insulating material, the emitter tube quickly heats to temperatures far beyond normal which it is capable of handling and often emitter tube failure will occur quickly thereafter.
In U.S. Pat. 4,044,751 by Arthur C. W. Johnson, filed May 19, 1975 and issued May 30, 1977 and assigned to the Combustion Research Corporation, the inventor describes a radiant energy heating system with power exhaust and excess air inlet. The object of the invention was to reduce the inlet and emitter tube temperature in order to reduce oxidation of the emitter tube and also to ensure that structural integrity was maintained of the emitter tube and also to be able to use lighter strength and thinner gauge emitter tubes in order to reduce the cost of radiant tube heaters. The patent does not discuss the possibility of using this technique for producing a more uniform temperature profile along the length of the emitter tube, but rather is essentially concerned with reducing the emitter end temperature in order to avoid material breakdowns.
It is desirable to have a radiant heater system having a more uniform emitter tube, temperature profile along its length in order to provide for more uniform heating particularly in spaces requiring very long emitter tubes. The more uniform the temperature profile along the emitter tube the more uniform heating can be achieved. In some instances, uniformity of temperature is highly critical, as for example in animal confinement and/or other applications.